The present invention relates to an article carrying-out monitor that inspects the presence of contamination (radioactive contamination), by radioactive substances, on an article, which is a subject of inspection carried out into a non-controlled area from a controlled area of a facility, in which radioactive substances are handled, such as an atomic power plant, etc.
As a conventional technology related to an article carrying-out monitor for an article to be inspected, article carrying-out monitors, for which a small article is especially a subject of inspection, are known as described in, for example, Japanese Patent No. 3475633 (Title of the Invention: Small article monitor) and JP-A-6-174852 (Title of the Invention: Small article carrying-out monitor apparatus). A small article is an article, such as tool, measuring instrument, document, notebook, etc., which is carried out into a non-controlled area by a person leaving a controlled area of radiation.
The small article monitor described in Japanese Patent No. 3475633 includes detectors in all six, that is, front and rear, left and right, and upper and lower directions as viewed in a running direction in a monitor chamber. Front and rear detection parts are mounted inside, for example, an inlet door and an outlet door so as to be capable of elevation as a small article 1 advances. Also, an upper surface detection part is positioned in a vertical direction according to height of a small article so as to enable assuming an appropriate sensitivity and the presence of contamination is detected after positioning is made.
The small article carrying-out monitor apparatus described in JP-A-6-174852 includes detectors in all six, that is, front and rear, left and right, and upper and lower directions as viewed in a running direction in a monitor chamber and is arranged in the monitor chamber such that a small article is moved up and down from under as shown in FIG. 9 of JP-A-6-174852.
As described above, a small article is an article, such as tool, measuring instrument, document, notebook, etc., which is not fixed in size and shape. With the conventional technology described in Japanese Patent No. 3475633, since positioning in a vertical direction is done so as to provide for an optimum position according to a height of a small article, contamination is surely detected in the case where contamination is present on an upper surface or a lower surface of the small article, but there is a fear that a weak radiation cannot be detected because of no positional adjustment on front and rear, and left and right surfaces. Such problem is likewise involved in the conventional technology described in JP-A-6-174852.
As radiation control becomes stricter (control in conformity to the control criteria of 0.8 Bq/cm2 for Co-60) in the future, there is a need of surely detecting radioactive surface contamination on all surfaces of a subject of inspection.
Also, there is a demand for a further improvement in sensitivity of radiation detection by means of lowering of the limit of detection. Generally, there is a need of reducing influences by background noise in order to achieve an improvement in detection sensitivity. Further, there is a demand for elimination of an erroneous determination that a small article, to which natural, nuclear species adhere widely and thinly and which is not contaminated, is determined to be “contaminated”.
In view of the above, it would be desirable to provide an article carrying-out monitor that eliminates influences by a shape of an article, which is a subject of inspection, as far as possible and improves detection of six surfaces of the article, which is a subject of inspection, in sensitivity to enable favorably detect the presence of contamination.